.Iadd.I. Field of the Invention
The present invention concerns a respiratory mask. The mask is useful in cold weather for heating and humidifying inhaled air with exhaled air through a heat exchanger.
II. Description of Known Art .Iaddend.
The detrimental effects of breathing cold air, particularly for people with medical problems such as cardiac conditions, angina, and asthma, and the benefits of heating inhaled air have been recognized for many decades and are described in various publications including U.S. Pat. Nos. 3,835,853; 4,325,365; 4,601,287; 4,793,343; and 4,829,997. Inhaled air has been heated with electrical elements as taught in U.S. Pat. Nos. 2,626,343; 3,249,108; 4,601,287; 4,620,537; and 4,793,343.Iadd., .Iaddend.and with heated water as taught in U.S. Pat. No. 5,086,766. Inhaled air has been heated also by devices that obtain heat from portions of the human body rather than external power sources as described ..is.!. .Iadd.in .Iaddend.U.S. Pat. Nos. 4,269,183, 4,473,071, 4,671,268, and 4,683,869. The advantage of heating the inhaled air with humid exhaled air has been recognized for many decades. U.S. Pat. Nos. 3,326,214, 3,333,585, 3,814,094, and 4,136,691, .Iadd.and .Iaddend.4,478,215 teach heating and humidifying inhaled air through exhaled air by passing the air through an exchanger fabricated from either foil, a nonwoven resilient porous fibrous organic polymeric material, a foraminous ..heat conductive.!. .Iadd.heat-conductive .Iaddend.material, or a continuous strip of wire netting wound helically. In addition, U.S. Pat. Nos. 4,150,671, 4,196,728, 4,200,094, 4,325,365, and 4,458,679 teach heating inhaled air with ..one of.!. the following: a conduit having heat-exchanging fins; a flexible curved horn of expanding cross section, having a flared internal chamber containing metal mesh; a spool-like member having a series of transverse notches which leave integral fins; an elongated curved housing in which is disposed a plurality of pairs of spaced-apart vanes; or a counter-current medium such as a metal sponge. U.S. Pat. No. 3,835,853 teaches an improved device for heating inhaled air with exhaled airs which avoids ice formation at very low temperatures by bypassing a portion of the inhaled air with an automatic valve. Some of these patents, e.g., U.S. Pat. No. 4,478,215, teach that the inhaled air is humidified as well as heated by the exhaled air.
None of the disclosed devices for heating air for breathing is in widespread use. Generally.Iadd., .Iaddend.the effective devices are heavy and bulky. In addition, many are relatively costly to produce.
.Iadd.Furthermore, these additional U.S. patents are cited:
U.S. Pat. No. 2,381,568--Gas Mask. PA1 U.S. Pat. No. 2,741,246--Gas Masks. PA1 U.S. Pat. No. 5,007,114--Humidity-retaining Mask. PA1 U.S. Pat. No. 5,010,594--Dampening Mask for Use in Aircraft. PA1 U.S. Pat. No. 5,433,192--Breathing Mask having a Cellulose Heat and Moisture Exchanger Formed Therein. PA1 U.S. Pat. No. 5,595,173--Rehumidification Filter for Ventilation Mask. PA1 U.S. Pat. No. 5,435,299--Respiratory Mask.